Same connectivity, two 3-D shapes — the difference wedges and dashes record.
A tetrahedral carbon with four different groups can be arranged two mirror-image ways that a flat drawing can't tell apart; wedge-and-dash bonds record which groups point toward you and which point away — the one thing a plain line-drawing throws away.
1. A Wedge Comes Toward You; a Dash Goes Behind
Three marks, three directions: a plain line lies in the plane, a solid wedge rises toward your eye, and a hashed wedge sinks behind the page — the paper is a window and the wedges say which atoms sit in front of the glass.
2. Wedge and Dash Show the 3-D Shape at a Tetrahedral Carbon
An sp3 carbon's four bonds splay to the corners of a tetrahedron, so the convention draws two as in-plane lines, one wedge, and one dash to reconstruct that shape on a flat page.
3. The Narrow End of the Wedge Always Sits on the Stereocenter
The pointed end anchors at the stereocenter and the wide end is the atom coming toward you — the dash fans the same way — so reversing it accidentally draws the mirror image.
4. Wedge and Dash Encode Configuration, Which Becomes R or S
The marks fix the configuration: rank the groups by CIP priority, point the lowest (usually H on the dash) away, and trace 1→2→3 — clockwise is R, counterclockwise is S.
5. Swapping Any Two Groups Inverts the Configuration
A single swap of any two groups inverts the configuration and a second swap restores it — so redraw in pairs, or you turn a molecule into its enantiomer.
6. Wedges Reappear in Chairs, Fischer Projections, and Haworth Rings
Chair axial/equatorial bonds, Fischer horizontals (toward you) and verticals (away), and Haworth above/below are all this same front/back idea reused — while a wavy line means the configuration is left unspecified.
7. Summary
Solid = toward you · dashed = away · line = in plane · two in-plane bonds + one wedge + one dash, narrow ends on the center · read R/S with lowest priority away · one swap inverts, so redraw in pairs.
Quiz yourself
Tap a question to reveal the answer — free, no login.
The narrow, pointed end. The point is anchored on the near carbon (the stereocenter), and the wide end is the atom coming out of the page toward you. The hashed wedge follows the same rule: thin end at the stereocenter, fanning wider as it recedes behind the page.
Different — you have drawn the opposite enantiomer. Flipping one bond from behind the page to in front of it is a single swap, and one swap inverts the configuration (R becomes S). To keep the same molecule while redrawing, you must make swaps in pairs.
Because H is almost always the lowest CIP priority, and R/S is read with the lowest priority pointing away from you. Putting H on the dash means it already points behind the page, so you can trace the remaining three groups 1→2→3 directly — clockwise is R, counterclockwise is S — with no mental rotation.
Two — one wedge and one dash — with the other two drawn as plain in-plane lines. That combination reconstructs the tetrahedron unambiguously. Drawing all four as wedges is meaningless, and drawing none hides the stereochemistry on a carbon that has it.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.